A blood collecting tube of the type shown in FIG. 7 has heretofore been used for blood collection which is typically performed in clinical or biochemical testing. FIG. 7 is a cross-sectional view of a conventional type of blood collecting tube before use while FIG. 8 is a cross-sectional view of the same blood collecting tube after use. In the general form of usage, the blood collecting tube is combined with a holder 12 provided with a needle 16 having opposite sharp-pointed ends.
As shown in FIG. 7, s blood collecting tube 10 includes a tubular body 11 and a plug 14 fitted into the opening of the tubular body 11. In general, the tubular body 11 is formed of a material such as glass or a transparent resin, and the plug 14 is made of a rubber material such as vulcanized butyl rubber. The pressure inside the tubular body 11 is maintained in a reduced state. It is possible to stick a hollow needle into the plug 14 as described later and, the addition, it is necessary to maintain the liquid-tightness of the blood collecting tube 10 by stopping up the needle hole which may remain after the hollow needle has been extracted therefrom. In this respect, it has hitherto been considered suitable to use the plug 14 made of a sealing material such as rubber.
On the other hand, a blood collecting holder 12 has a cylindrical holder body 15 which is open at its lower end, and a hollow needle 16 is attached to the upper end portion of the holder body 15. Attachment of the needle 16 is performed by screwing a hub 17 of the needle 16 onto a threaded portion 18 which is formed on the upper end portion of the holder body 15. The forward end 16A of the needle 16 is provided with a shart-pointed end which is so formed as to pierce the skin while the rearward end 16B of the needle 16 is provided with a sharp-pointed end capable of piercing the plug 14 attached to the tubular body 11. In addition, the rearward end 16B is enclosed in a sheath-like resilient body; for example, a rubber tip 19.
In a case where blood is to be collected using the blood collecting tube 10 and the blood collecting holder 12 each having the aforesaid construction, the forward end 16A of the needle 16 secured to the holder 12 is first stuck into a blood vessel. The blood collecting tube 10 is then inserted into the holder body 15. As shown in FIG. 8, at this time, the needle 16 is stuck through the rubber tip 19 and then into the plug 14 fitted into the blood collecting tube 10, and thus the hollow needle 16 is stuck at its rearward end 16B into the interior of the tubular body 11 having a reduced level of internal pressure. In this state, the rubber tip 19 is collapsed in a bellows-shaped form in the space between the plug 14 and the holder body 15. In consequence, it becomes possible to introduce blood through the forward end 16A of the hollow needle 16 toward the rearward end 16B thereof owing to the fact that the internal pressure of the blood collecting tube 10 is maintained in a reduced state. The thus-introduced blood is allowed to flow into the blood collecting tube 10 and this completes the blood collection.
When a predetermined amount of blood is collected in the interior of the blood collecting tube 10, the blood collecting tube 10 is removed from the holder 12 in the direction indicated by an arrow B (refer to FIG. 8). In this state, the shape of the rubber tip 19 is restored to its original form. If an additional quantity of blood is to be collected, a new tubular body 11 may be inserted into the holder body 15. After completion of the blood collection, the blood collecting holder 12 is removed from the skin.
It is to be noted that the internal pressure of the blood collecting tube 10 is not necessarily be maintained in a reduced state.
In order to take the thus-collected blood out of the blood collecting tube 10 having the aforesaid construction for the purpose of testing, it is necessary to perform an operation termed "unplugging" that is, the plug 14 (such as a rubber plug) needs to be extracted from the opening of the tubular body 11 utilizing a strong force. However, in a case where the plug 14 is formed of a resilient material such as rubber, the operation termed "unplugging" involves various problems; for example, shock which may be produced upon removal of the plug 14 from the tubular body 11 might cause the blood clinging to the tubular body 14 to scatter in the air or to be transferred to the user's hands or the like. There is therefore a strong demand for a solution to this problem. Also, an attempt at extracting blood without removing the plug 14 from the tubular body 11 is made in an automatic testing system. However, even if a needle is to be directly stuck through the plug 14 without removing it from the tubular body 11, the needle is bent due to the large thickness of the rubber plug 14, and this phenomenon makes it difficult to realize such an attempt.
In addition, when the aforesaid blood collecting tube 10 in which the internal pressure is reduced is to be produced in a factory, the pressure within the tubular body 11 is commonly preset at a suitably reduced level in accordance with the amount of blood to be collected. The thus-produced blood collecting tube 10 is commonly stored near the user in a hospital or a doctor's office until it is used. Although the blood collecting tube 10 is stored for a different period by each user, the tube 10 may be stored for as long as 2-3 years. While the blood collecting tube 10 is being stored over such an extended period of time, the air may enter the tube 10 through the portion occupied by the plug 14. In this case, the degree of reduction in the pressure in the blood collecting tube 10 cannot be correctly maintained, and thus, even if such a tube 10 is used in blood collection, it is difficult to collect a predetermined amount of blood. For this reason, in order to assure the air-tightness of the blood collecting tube 10 during storage thereof, various methods have heretofore been considered; for example, the thickness of the plug 14 is increased, or the composition of rubber material is considered. However, if the thickness of the plug 14 is increased, it becomes difficult to stick the needle 16 thereinto, and this may force the operator to do an awkward operation.
Also, the external appearance of the blood collecting tube 10 having the aforesaid plug 14 for the tubular body 11 does not change when putting back the plug 14 in its place after removing it once, and thus, there is a chance using the blood collecting tube 10 whose degree of reduction of the pressure is not correctly maintained for collecting the blood.
It is therefore an object of the present invention to provide a blood collecting tube which is easy to handle without involving the need for a so-called unplugging operation which includes the step of removing the plug from the opening of the tubular body.
It is another object of the present invention to provide a blood collecting tube which is capable of maintaining its air-tightness during the period from production to use and which can be pierced with a hollow needle, as well as being capable of maintaining liquid-tightness even after extraction of the hollow needle.